Cerium oxide powder is a highly functional ceramic material that is widely used in abrasives, catalysts, phosphors and the like. Recently, it has been widely used as an abrasive for a chemical mechanical polishing for the selective planarization of semiconductor substrates. General methods for preparing such cerium oxide powder include a vapor-phase process, a solid-phase process, a liquid-phase method, and the like.
Methods of preparing cerium oxide powder through the vapor-phase process are methods of directly preparing cerium oxide powder by vaporizing a cerium precursor and then reacting the vaporized material with oxygen or the like. These methods include a decomposition method by flame combustion, a decomposition method by gas condensation, a plasma decomposition method, a laser vaporization method, and the like. However, these methods have a problem in that it is difficult to prepare cerium oxide powder in large scale because cerium salt precursor and equipment need high cost.
Methods of preparing cerium oxide powder through the solid-phase process comprise calcining process of the raw material of cerium oxide, such as carbonate, sulfate, oxalate or the like. International Patent Publication Nos. WO 1998/14987 and WO 1999/31195 disclose cerium oxide abrasives for polishing silicon oxide insulating films, which are prepared by calcining cerium carbonate powder having large particle size in an oxygen atmosphere to prepare cerium oxide powder having a size of 30-100 μm, and then controlling the particle size of cerium oxide by dry milling and wet milling processes. However, these methods have problems in that cerium oxide powder having large particle size remains even after the milling processes, making it difficult to control the particle size of cerium oxide, and thus a filtration process using a filter should be additionally carried out for a long period of time, even after a CMP slurry is finally prepared.
Methods of preparing cerium oxide powder through the liquid-phase process are methods of preparing cerium oxide powder directly from a starting material of trivalent or tetravalent cerium salt by adding a pH modifier such as ammonia. These methods include a precipitation method and a hydrothermal synthesis method, and studies thereon are being actively conducted, because relatively low raw material cost and equipment cost are incurred. However, the reaction between starting materials used in the preparation of cerium oxide easily occurs from a nucleation step, making it difficult to control particle growth. Also, when cerium oxide powder prepared through the liquid-phase process is used for polishing, it will have low polishing rate.